The present invention relates to a process for re-starting a previously interrupted spinning process in a spinning arrangement, which arrangement comprises a drafting unit which can be shut down and an airjet unit comprising a vacuum chamber, whereby, for the purpose of removing an initially inhomogenous fiber stream, a staple fiber strand, delivered by the re-operating drafting unit, is temporarily suctioned as waste via a deflecting device after it has left the drafting unit, the staple fiber strand being joined with a thread which is transported through the airjet unit only when a homogenous fiber stream has formed.
The present invention relates further to a spinning arrangement for carrying out the process, comprising a drafting unit which can be shut down, also comprising an airjet unit having a fiber feed channel, a thread withdrawal channel and a vacuum chamber, also comprising a deflecting device for temporarily deflecting a staple fiber strand, delivered by the drafting unit, from a thread to be joined thereto.
A process and an arrangement of this type is prior art in the international published application WO 94/00626. This publication refers in general to airjet spinning arrangements without their specific embodiments and deals with the re-starting of a previously interrupted spinning process, when, for example an end break occurs for some reason. In this case, the end of an already spun thread must be first guided back to the drafting unit after an interruption in the spinning process has occurred. The shut down drafting unit can then be set in operation again and the newly delivered staple fiber strand be joined to the end of the thread. Because the staple fiber strand has been torn in the drafting unit due to the interruption in the spinning process and the associated shutting down of the drafting unit, a staple fiber strand forms when the drafting unit is operating again which is initially relatively inhomogeneous at its start. For this reason, it is provided in the known process and in the known spinning arrangement that the initially inhomogeneous fiber stream is temporarily sucked off as waste and not immediately joined with the end of the thread fed back to the drafting unit. Only after a homogeneous fiber stream is formed is the staple fiber strand joined with the thread transported through the airjet unit. This permits the creation of a joining point of significantly improved quality for the joining process—so-called piecing—of the re-delivered staple fiber strand with the thread, in that, instead of an arbitrarily produced initial piece of the staple fiber strand caused by tearing, a newly generated initial piece of the staple fiber strand is joined with the thread, whereby the new initial piece is generated from a fiber stream which is homogeneous again. A suction tube located between the drafting unit and the airjet unit serves for the temporary suction of the inhomogeneous fiber stream.
In non-generic European published patent 0 807 699, the piecing of a staple fiber strand to the end of a thread in a very specific airjet spinning arrangement is known. In the case of this spinning arrangement, the drafted staple fiber strand is first fed through a fiber feed channel of the airjet unit into a vortex chamber, to which a fluid device is arranged for generating a vortex current around the entry opening of a thread withdrawal channel. Initially, the front ends of the fibers held in the staple fiber strand are guided into the thread withdrawal channel, while rear free fiber ends spread out, are seized by the vortex current and wound around the front ends already located in the entry opening of the thread withdrawal channel, that is, around the front ends already bound in, whereby a thread with a mostly real twist is formed. In this known spinning arrangement also, the initial piece of the delivered staple fiber strand is at first subjected to suction after the drafting unit is operational again, however in a suction tube located between the drafting unit and the airjet unit and, in addition, together with the end of the thread with which the staple fiber strand is to be joined. The initial piece of the staple fiber strand and the end of the thread fed back to the drafting unit are stored temporarily in one and the same suction device. Thus, a relatively arbitrary connection of the suctioned staple fiber strand with the likewise suctioned thread is formed, whereby a good quality piecing point is not specifically targeted. In the case of a spinning arrangement of this type in a real embodiment, a splicing arrangement is provided—which is not mentioned in the publication—which subsequently cuts out the connecting point after piecing of the staple fiber strand to the thread and replaces it with a splice point of better quality.
It is an object of the present invention in the case of a process and a spinning arrangement of the above mentioned type to create a homogeneous fiber stream and to carry out the joining of the fiber staple strand with the end of the thread in a particularly effective way.
This object has been achieved in that the inhomogeneous fiber stream is removed with the aid of a vacuum prevailing in the vacuum chamber.
In the case of the spinning arrangement, the object of the present invention is achieved accordingly in that the vacuum chamber is incorporated into the deflecting device. The vacuum chamber is connectable to the drafting unit via a connecting channel.
Due to of the features of the present invention, the inhomogeneous fiber stream is not deflected by an external suction device, but rather a device already present in the spinning arrangement is used to remove the inhomogeneous fiber stream. The vacuum chamber in the airjet unit is needed during normal operation in order to evacuate the compressed air fed to the vortex chamber and simultaneously to transport away the inevitable fiber waste unavoidable in this spinning process. This vacuum can be utilized for the purposes of the present invention to initially deflect the inhomogeneous fiber stream from the end of thread, with which a homogeneous fiber stream is then joined. The vacuum present in the vacuum chamber during operation is advantageously increased temporarily in order to remove the inhomogeneous fiber stream. Thus, the inhomogeneous fiber stream is easier to deflect from its operational transport path, as travelled during the normal spinning process. With correct timing, the overlapping area of the initial piece of the homogeneous fiber stream with the end of the thread can be kept very narrow, so that only a very small slub occurs, which can be regarded as an acceptable fault not visible in the end product, for example in woven material.
In one variation, it is provided that the staple fiber strand is deflected from its operational transport path inside the airjet unit. Initially, the inhomogeneous fiber stream thus enters into the inside of the airjet unit as in normal spinning operation, and is however temporarily deflected as waste therein. As a result, the piecing of the homogeneous fiber stream to the end of the thread also takes place in the inside of the airjet spinning unit, as soon as the temporarily increased low pressure is reduced again to the normal level for the spinning process.
In a further variation, it is provided that the staple fiber strand is deflected between the drafting unit and the airjet unit from its operational transport path. The inhomogeneous fiber stream travels temporarily not on its normal path into the inside of the airjet unit, but rather in another way. This is purposeful because the entry opening into the airjet unit usually has very small dimensions and therefore the fiber mass, including the piecing thread, cannot be threaded correctly through this small opening, in particular in the case of coarse yarns and high delivery speeds. In this case, the joining of the homogeneous fiber stream with the end of the thread partly takes place before the airjet unit is reached.
In order that the amount of inhomogeneous fiber stream discharged as waste is kept as small as possible, it is advantageously provided in the embodiment of the present invention that the fiber mass of the staple fiber strand during the removal of the inhomogeneous fiber stream is reduced. The staple fiber strand is fed from the drafting unit initially at a reduced delivery speed, whereby in this way also, due to the deflection of the staple fiber strand from the normal transport path, a homogeneous fiber stream is achieved after a certain length of time.
Although in the course of the present invention, the end of the thread to be pieced, which is fed back to the drafting unit, is fed back through the delivery roller pair of the drafting unit, it should be expressly pointed out that the end of the thread can also be held ready between the airjet unit and the drafting unit in a practical way.
In the spinning arrangement according to the present invention, it is advantageously provided that the vacuum chamber is equipped with a connecting element for temporarily increasing the low pressure. This can be, for example, a suction connection, which can be connected to a separate low pressure source, which is either stationary or applied to a travelling maintenance device. It is advantageously provided however, that the connecting element comprises an injector channel which can be charged with compressed air. This is a particularly effective way to increase the low pressure, especially as a compressed air injection is advantageous for the piecing process in any case.
In the case of the vacuum chamber connected to the drafting unit, a connecting channel can, in one variation, be the fiber feed channel, used in the regular spinning process, from which the thread withdrawal channel can preferably be separated. This is a simple solution without any complicated additional technical steps, especially as the separation of the thread withdrawal channel from the fiber feed channel for threading the thread and for cleaning the vortex chamber is advantageous in any case.
Particularly advantageous is, however, a separate bypass channel. This is advantageously provided in one variation with a closing device, which closes the bypass channel during the normal spinning process, while opening it for the purposes of deflecting the inhomogeneous fiber stream. A travelling maintenance device can actuate this process.
In a further variation, a cleaning channel directed against the drafting unit during operation can function as the bypass channel. In this case, the bypass channel does not need to be closed during operation, as the delivery roller pair of the drafting unit is constantly cleared of fiber fly by way of suction action via this bypass channel. In order to deflect the inhomogeneous fiber stream, the low pressure in the vacuum chamber can be temporarily increased, so that the fiber stream is deflected easily from its normal transport path by way of the cleaning channel.